1. Field of the Invention
The present invention relates to a sheet material stacking device, and more particularly, it relates to a sheet material stacking device having a function for stacking sheet materials on a stacking tray and applicable to an image forming apparatus such as a copying machine, a printer, a facsimile and the like.
2. Related Background Art
In conventional image forming apparatuses such as copying machines, printers, facsimiles and the like, there is provided a stacking tray on which sheet materials discharged from a main body of the image forming apparatus are stacked, and an example of such an image forming apparatus is shown in FIG. 6. In FIG. 6, the reference numeral 201 denotes a main body of the image forming apparatus; 210 denotes a sheet material stacking device; and 222, 251, 252, 253, 254 and 255 denote stacking trays on which sheet materials discharged and sorted from the sheet material stacking tray 210 are stacked. In order to minimize the installation space of the system, the stacking trays 251 to 255 include extensible/retractable extension trays 261 to 265, respectively.
However, the above-mentioned conventional example has the following problems.
That is to say, thicknesses of the stacking trays 251 to 255 must be increased to hold the extension trays 261 to 265 therein. More particularly, the thickness of each stacking tray is required to be not less than 12 mm.
Particularly when the number of the stacking trays is increased, the total height of the apparatus will be increased accordingly. To avoid this, there has been proposed a technique in which each of extension trays 361 is disposed at one side (upper side) of each of the stacking trays 351, 352, as shown in FIG. 7. However, with this arrangement, a leading end of a sheet material 300 discharged from a main body 210 by a pair of rollers 353 of an image forming apparatus may be caught by an upstream end 361a of the extension tray 361.
Further, when the stacking trays are arranged conversely (i.e., the extension trays are disposed at lower sides of the stacking trays), if an upwardly curled sheet material is discharged onto the extension tray of the lower stacking tray, the leading end of the sheet material may be caught by the upstream end of the extension tray of the upper stacking tray, thereby causing the sheet jam.